Assessing El Niño Impact on Climate Anomalies

This page allows the user to plot current
or historical climate anomalies,
and compare those to the linear signal associated with El Niño.

Monthly mean geopotential height at 500 mb is available from January 1948 thru April 2002,
while Outgoing Longwave Radiation (OLR) is available from June 1974 to April 2002.
By selecting a variable and a time-averaging
interval, the observed anomaly for that period is calculated.
Anomalies are computed using a 1958-1997 base climatology (1974-1997 for OLR).
The OLR anomalies are displayed as rainfall anomalies in mm/day using the Arkin and
Meisner (1987) empirical relation.

El Niño's contribution to the observed anomalies is
determined by regressing the historical
monthly anomalies of each variable onto the equatorial Pacific
EOF1 SST time series for 1948-2002 (1974-2002 for OLR). For each variable, there are
12 regression maps, one for each calendar month. For the time-averaging period selected by
the user, the corresponding monthly regressions are weighted by the amplitude of the EOF1
principal component and then linearly averaged.